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Sharing pathogens The way bacteria transfer between possums may offer some insight into the spread of human epidemics, according to a new Australian study published.

Scientists from the Australian National University (ANU) looked at how social interactions between mountain brushtail possums influenced the transfer of the bacterium, Escherichia coli.

Surprisingly they found it was not just how much time the possums spent in contact with each other that determined the spread of E. coli, but rather what they were doing when they interacted.

"We originally started out thinking daytime den sharing would be important and that disease transfer might be a reason why individuals in some populations were less likely to share dens," says lead researcher Dr Michaela Blyton.

"But then we found that it is actually the night time foraging interactions that were more important."

E. coli is typically thought of as an environmental pathogen that is spread through ingestion of water or food that has been contaminated by faeces. But Blyton says the results, appearing in the journal Ecology Letters, indicate social interactions also play an important role.

"It suggests that the close contact of those individual possums facilitates transfer more than just the environment itself."

Blyton and her colleagues measured the level of social interaction between the possums by fitting more than 30 individuals with collars, which recorded when the possums came within three metres of each other.

The collars also contained radio transmitters that allowed the scientists to track the specific location of the possums through the Victorian high country.

More than 100 strains of E. coli were identified among the possums, making it possible to map how different strains were shared between individuals.

Humans implications

Blyton says that while possums were the subject of the study, the results have implications for humans as well.

"Humans carry E. coli in remarkably similar ways to possums. Most individuals will be carrying an E. coli strain at any given time."

Most strains of E. coli are not harmful, but some strains can cause gastroenteritis. Others cause illness when they get into wrong parts of the body, such as the bladder or the blood.

As E. coli is widely used as a model for other gastrointestinal pathogens, Blyton says the results could also be used to predict the spread of more virulent pathogens.

Dr Samuel Banks, also from ANU and co-author of the study, says the findings highlight the importance of understanding how pathogens spread within a population.

"It is not enough to assume pathogens spread between individuals because they live near one another or because they are close to each other. There are very specific pathways by which transmission happens."